diff --git a/b9.cabal b/b9.cabal
--- a/b9.cabal
+++ b/b9.cabal
@@ -1,5 +1,5 @@
 name:                b9
-version:             0.5.4
+version:             0.5.5
 
 synopsis:            A tool and library for building virtual machine images.
 
@@ -120,7 +120,7 @@
                     , GADTs
   hs-source-dirs:    src/lib
   default-language:  Haskell2010
-  ghc-options:       -O3 -with-rtsopts=-N -Wall
+  ghc-options:       -with-rtsopts=-N -Wall -fno-warn-unused-imports
                      -fwarn-unused-binds -fno-warn-unused-do-bind
 
 executable b9c
@@ -133,7 +133,7 @@
                    , optparse-applicative
   hs-source-dirs:    src/cli
   default-language:  Haskell2010
-  ghc-options:       -O3 -threaded -with-rtsopts=-N -Wall -Wall
+  ghc-options:       -threaded -with-rtsopts=-N -Wall -fno-warn-unused-imports
                      -fwarn-unused-binds -fno-warn-unused-do-bind
 
 test-suite spec
diff --git a/src/lib/B9/B9Monad.hs b/src/lib/B9/B9Monad.hs
--- a/src/lib/B9/B9Monad.hs
+++ b/src/lib/B9/B9Monad.hs
@@ -28,6 +28,7 @@
 import           System.Exit
 import           System.FilePath
 import           System.Random ( randomIO )
+import qualified System.IO as SysIO
 import           Text.Printf
 import           Control.Concurrent.Async (Concurrently (..))
 import           Data.Conduit (($$))
@@ -39,6 +40,7 @@
                              , bsCfgParser :: ConfigParser
                              , bsCfg :: B9Config
                              , bsBuildDir :: FilePath
+                             , bsLogFileHandle :: Maybe SysIO.Handle
                              , bsSelectedRemoteRepo :: Maybe RemoteRepo
                              , bsRemoteRepos :: [RemoteRepo]
                              , bsRepoCache :: RepoCache
@@ -55,11 +57,18 @@
 run cfgParser cfg action = do
   buildId <- generateBuildId
   now <- getCurrentTime
-  bracket (createBuildDir buildId) removeBuildDir (run' buildId now)
+  withBuildDir buildId (withLogFile . run' buildId now)
 
   where
-    run' buildId now buildDir = do
-      maybe (return ()) setCurrentDirectory (buildDirRoot cfg)
+    withLogFile f =
+      maybe (f Nothing)
+            (\logf -> SysIO.withFile logf SysIO.AppendMode (f . Just))
+            (logFile cfg)
+
+    withBuildDir buildId = bracket (createBuildDir buildId) removeBuildDir
+
+    run' buildId now buildDir logFileHandle = do
+      maybe empty setCurrentDirectory (buildDirRoot cfg)
       -- Check repositories
       repoCache <- initRepoCache (fromMaybe defaultRepositoryCache (repositoryCache cfg))
       let remoteRepos = getConfiguredRemoteRepos cfgParser
@@ -70,6 +79,7 @@
                   cfgParser
                   cfg
                   buildDir
+                  logFileHandle
                   selectedRemoteRepo
                   remoteRepos'
                   repoCache
@@ -79,19 +89,20 @@
           buildDate = formatTime undefined "%F-%T" now
           selectedRemoteRepo = do
             sel <- repository cfg
-            (lookupRemoteRepo remoteRepos sel
+            lookupRemoteRepo remoteRepos sel
              <|> error
                    (printf
                       "selected remote repo '%s' not configured, valid remote repos are: '%s'"
                       sel
-                      (show remoteRepos)))
+                      (show remoteRepos))
       (r, ctxOut) <- runStateT (runB9 wrappedAction) ctx
       -- Write a profiling report
       when (isJust (profileFile cfg)) $
-        writeFile (fromJust (profileFile cfg)) (unlines $ show <$> (reverse $ bsProf ctxOut))
+        writeFile (fromJust (profileFile cfg))
+                  (unlines $ show <$> reverse (bsProf ctxOut))
       return r
 
-    createBuildDir buildId = do
+    createBuildDir buildId =
       if uniqueBuildDirs cfg
         then do
           let subDir = "BUILD-" ++ buildId
@@ -105,7 +116,7 @@
           canonicalizePath buildDir
 
       where
-        resolveBuildDir f = do
+        resolveBuildDir f =
           case buildDirRoot cfg of
             Nothing ->
               return f
@@ -184,11 +195,11 @@
   where
     getCmdLogger = do
       lv <- gets $ verbosity . bsCfg
-      lf <- gets $ logFile . bsCfg
-      return $ \level -> (CL.mapM_ (logImpl lv lf level . B.unpack))
+      lfh <- gets bsLogFileHandle
+      return $ \level -> CL.mapM_ (logImpl lv lfh level . B.unpack)
 
     checkExitCode ExitSuccess =
-      traceL $ "COMMAND SUCCESS"
+      traceL "COMMAND SUCCESS"
     checkExitCode ec@(ExitFailure e) = do
       errorL $ printf "COMMAND '%s' FAILED: %i!" cmdStr e
       liftIO $ exitWith ec
@@ -208,15 +219,17 @@
 b9Log :: LogLevel -> String -> B9 ()
 b9Log level msg = do
   lv <- gets $ verbosity . bsCfg
-  lf <- gets $ logFile . bsCfg
+  lfh <- gets bsLogFileHandle
   modify $ \ ctx -> ctx { bsProf = LogEvent level msg : bsProf ctx }
-  B9 $ liftIO $ logImpl lv lf level msg
+  B9 $ liftIO $ logImpl lv lfh level msg
 
-logImpl :: Maybe LogLevel -> Maybe FilePath -> LogLevel -> String -> IO ()
-logImpl minLevel mf level msg = do
+logImpl :: Maybe LogLevel -> Maybe SysIO.Handle -> LogLevel -> String -> IO ()
+logImpl minLevel mh level msg = do
   lm <- formatLogMsg level msg
   when (isJust minLevel && level >= fromJust minLevel) (putStr lm)
-  when (isJust mf) (appendFile (fromJust mf) lm)
+  when (isJust mh) $ do
+    SysIO.hPutStr (fromJust mh) lm
+    SysIO.hFlush (fromJust mh)
 
 formatLogMsg :: LogLevel -> String -> IO String
 formatLogMsg l msg = do
diff --git a/src/lib/B9/Builder.hs b/src/lib/B9/Builder.hs
--- a/src/lib/B9/Builder.hs
+++ b/src/lib/B9/Builder.hs
@@ -57,7 +57,7 @@
 buildArtifacts artifactGenerator cfgParser cliCfg =
   withB9Config cfgParser cliCfg $ \cfg ->
     run cfgParser cfg $ do
-      traceL =<< liftIO getCurrentDirectory
+      traceL . ("CWD: " ++) =<< liftIO getCurrentDirectory
       infoL "BUILDING ARTIFACTS"
       getConfig >>= traceL . printf "USING BUILD CONFIGURATION: %v" . ppShow
       assemble artifactGenerator